It has been proposed heretofore to injection-mold synthetic-resin materials adapted to harden by chemical processes upon injection into a mold cavity, under the heat provided at the mold. Such substances include vulcanizable elastomers which are capable of crosslinking through the use of sulfur or other bridges, and thermosetting synthetic resins in which crosslinking takes place via functional groups provided on the synthetic-resin chains. The two types of materials and systems which combine features of both, can be described as thermally hardenable substances, i.e. substances which harden, set or cure at elevated temperatures.
In operating with such substances, care must be taken to prevent thermohardening of the flowable mass before it enters the mold cavity or mold cavities. In other words hardening of the synthetic resin or elastomer material in the distribution channels of the mold assembly must be prevented.
To this end, it has been proposed heretofore to provide the distribution channel on a plate mounted on or clamped against a mold half and in communication with the mold cavity, the plate being formed with cooling means, e.g. for the circulation of water or another coolant through the plate. Of course, this arrangement may prevent thermohardening of the synthetic resin mass in the distribution channels of the plate, but also may provide an undesirable cooling of the adjacent mold half so that the thermohardening process within the mold cavity does not occur efficiently. When no cooling is provided, the contact between the distribution or manifold plate and the mold half has the disadvantage that the heat transferred to the plate increases the tendency to setting within the distribution channels. A high temperature differential must thus be provided across the distribution plate and between the distribution plate and the adjoining mold half. It has already been shown that simple cooling of the distribution or manifold plate while the latter lies against the mold during the injection process is insufficient because of heat transfer to this plate.